In piping systems for conducting gaseous fluid e.g. natural gas from one place to another, e.g. in connection with producing, gathering, collecting, processing, and/or transporting the gas, the need generally arises for measuring gas flow characteristics. For instance, it is conventional to partially obstruct the bore of the piping at a selected site using an orifice plate, and to measure differential pressure using taps located immediately upstream and downstream of the orifice plate.
Occasionally, there is a need to change-out the orifice plate, either because mechanically or chemically effected corrosion has changed its orifice size and shape, rendering collected differential pressure data difficult to interpret, or system flow characteristics have changed, so that a differently sized and/or shaped orifice is wanted.
Accordingly, there has arisen in the prior art orifice fittings, i.e. orifice plate holders which can be permanently mounted in a piping system, and from which the orifice plate may be removed and replaced with only partial disassembly of the orifice fitting itself, and with no need to either completely dis-install the orifice fitting, nor to jack the piping apart at the orifice fitting or partially disassemble the piping system.
However, in most instances, the prior art orifice fittings have been manufactured using castings and/or forgings for the orifice fitting bodies and other major parts. That has contributed excess weight, bulk and expense to the devices, and has necessitated either that the manufacturer build ahead for inventory in order to be able to fill orders in a reasonable time, or it has meant a long delay between receipt of an order and shipment of the goods. All of this is less tolerable in the marketplace of today than it once was.
Further, in most instances, the prior art orifice fittings have been factory-supplied with end connections which require that the user fabricate pipe nipples to the opposite ends in the field. This can prove inconvenient or troublesome, especially where the installer damages the body while attempting to field-attach pipe nipples to its end connections. Further, this field work may unacceptably add to the cost of making the installation due to excess labor and inspection costs.